1. Field of the Invention
The present invention relates to a one way clutch used to a starter or an alternator with a clutch.
2. Description of the Related Art
FIG. 3 shows a front elevational view, partly in cross section, of a conventional one way clutch disclosed in, for example, Japanese Utility Model Publication No. 63-32422. FIG. 4 is a view showing a state that the clutch outer of the conventional one way clutch is chucked. Further, FIG. 5 is an enlarged view of the main portion of the clutch outer. In the figures, a clutch outer 1 as a cylindrical driving member coupled with the shaft of a not shown starting motor has cam surfaces 1a as a plurality of taper-shaped cutouts defined on the inner periphery thereof at equal intervals on a circumference.
A cylindrical clutch inner 2 as a driven member is disposed in the clutch outer 1 and defines a wedge-shaped space between the cam surfaces 1a on the inner periphery of the clutch outer 1 and the clutch inner 2. The clutch inner 2 has a pinion 3 at an end thereof which is meshed with the ring gear of a not shown engine. Friction rollers 4 as columnar rollers are movably disposed in the wedge-shaped spaces. Each of the friction rollers 4 is pressed in the narrower direction of the wedge-shaped space by a spring 5 interposed and contracted between the friction roller 4 and the clutch outer 1.
In the conventional one way clutch arranged as described above, when the starting motor is driven and the clutch outer 1 is rotated in the direction of an arrow A, the friction rollers 4 rotate and are forced into the wedge-shaped spaces, so that the friction rollers 4 act as wedges to cause the clutch outer 1 to be coupled with the clutch inner 2 by a friction force. As a result, the clutch outer 1, the clutch inner 2 and the friction rollers 4 are rotated together with each other. Thus, the ring gear of the not shown engine is driven through the pinion 3 disposed at the end of the clutch inner 2 so as to start the engine. After the start of the engine, the above coupling engagement is released, that is, the springs 5 are inversely urged by the friction rollers 4 to release the wedge action so that the clutch inner 2 and the pinion 3 are driven in idle.
In general, the inner periphery of the clutch outer 1 is integrally formed by cold forging, machining by a broaching machine or the like and then the cylindrical portion of the clutch outer 1 is cut by a lathe or the like. The shapes and locations of the respective portions of the clutch outer 1 must be managed with a pinpoint accuracy, respectively, with respect to the cam surfaces 1a for transmitting a force to the friction rollers 4. Therefore, when a cutting operation is carried out on the clutch outer 1, the portions of the cam surfaces 1a formed by cold forging or the like are usually chucked, that is, the other cylindrical portion of the clutch outer 1 is cut using the cam surfaces 1a as a machining reference (FIG. 4).
Since the cam surface 1a is formed to have a taper shape, the center P thereof is dislocated from the center O of the cylinder of the clutch outer 1 (FIG. 5). Since chucks 10 for chucking the portions of the cam surfaces 1a must cause the contact surfaces 10a thereof to come into intimate contact with the cam surfaces 1a, each contact surface 10a must be formed to a shape tracing the cam surface 1a, so that the center of the approximately arc-shaped contact surface 10a is dislocated from the center of rotation Q of the chuck. Consequently, it is not easy to machine the contact surfaces 10a of the chucks 10, and further since there are a plurality of the cam surfaces 1a, it is difficult to finish the individually machined chucks 10 with a pinpoint accuracy as a whole. In addition, since the cam surface 1a is formed to the taper shape, a skill is required to chuck the clutch outer 1 by a chucking jig without eccentrically locating it and thus the workability of a chucking job is not good.